ORIGIN OF THE DIAMOND 389
crystallization,
of the matrix in which it occurs, appears evident from the fact that
diamonds have been found in eclogite, itacolumite and an igneous rock.
Professor Bonney found ten small diamonds embedded in a bowlder of
eclogite from one of the Newlands pipes in Griqualand West. It is
reported also that they are found occasionally in the Roberts-Victor
mine in the same matrix. In Brazil though usually found in drift, they
occur to a limited extent in the itacolumite, thought to be the
original matrix, and which by decomposition furnished the
diamondiferous quartz pebble drift. Some geologists think that the
Semri sandstone of India was the matrix there, because many fragments
of it are found with the diamonds in the quartzose conglomerate which
is the diamondiferous material of some parts of India. A diamond was
found embedded in hornblende diabase at Oakey creek near Inverell,
Australia. The sparse occurrence of diamond crystals in unaltered
igneous rock, and their abundance in the kimber-lite breccia, suggests
that crystallization occurred during the metamorphosis by hydration of
an igneous magma composed of favorable reducing chemical constituents.
That the crystallization of carbon can, occur under intense heat and
pressure has been demonstrated by Professor Moissan, but that the heat
and pressure was applied in the same manner in the diamond chimneys
appears doubtful, for in them, the quantity of diamonds decreases with
the approach of the diamondiferous material to the source of heat, and
the associate minerals are chiefly silica and magnesia. A natural
solvent for carbon with sufficient heat to cause the necessary
chemical reactions, and pressure, is probably Nature's method of
crystallizing carbon.
